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<pre><span class="sourceLineNo">001</span><a name="line.1"></a>
<span class="sourceLineNo">002</span>/*<a name="line.2"></a>
<span class="sourceLineNo">003</span> * Copyright (C) 2011 Archie L. Cobbs. All rights reserved.<a name="line.3"></a>
<span class="sourceLineNo">004</span> *<a name="line.4"></a>
<span class="sourceLineNo">005</span> * $Id: GraphCloneable.html 740 2013-10-02 21:27:31Z archie.cobbs $<a name="line.5"></a>
<span class="sourceLineNo">006</span> */<a name="line.6"></a>
<span class="sourceLineNo">007</span><a name="line.7"></a>
<span class="sourceLineNo">008</span>package org.dellroad.stuff.java;<a name="line.8"></a>
<span class="sourceLineNo">009</span><a name="line.9"></a>
<span class="sourceLineNo">010</span>/**<a name="line.10"></a>
<span class="sourceLineNo">011</span> * Implemented by objects in an object graph that support &lt;i&gt;graph cloning&lt;/i&gt;, i.e., deep copies without<a name="line.11"></a>
<span class="sourceLineNo">012</span> * duplicates and preserving reference topology.<a name="line.12"></a>
<span class="sourceLineNo">013</span> *<a name="line.13"></a>
<span class="sourceLineNo">014</span> * &lt;p&gt;<a name="line.14"></a>
<span class="sourceLineNo">015</span> * Graph cloning creates a copy of an object graph that, like a normal deep copy, contains no references to objects in the<a name="line.15"></a>
<span class="sourceLineNo">016</span> * original object graph (except for immutables), but in addition, each {@link GraphCloneable} object is only copied once.<a name="line.16"></a>
<span class="sourceLineNo">017</span> * As a result the copy graph has the same reference topology as the original graph (with respect to all the<a name="line.17"></a>
<span class="sourceLineNo">018</span> * {@link GraphCloneable}s). In particular, reference cycles among {@link GraphCloneable}s are preserved and do not<a name="line.18"></a>
<span class="sourceLineNo">019</span> * cause infinite loops.<a name="line.19"></a>
<span class="sourceLineNo">020</span> * &lt;/p&gt;<a name="line.20"></a>
<span class="sourceLineNo">021</span> *<a name="line.21"></a>
<span class="sourceLineNo">022</span> * &lt;p&gt;<a name="line.22"></a>
<span class="sourceLineNo">023</span> * Graph cloning operates similar to a deep copy operation, except that graph cloning uses a {@link GraphCloneRegistry} to keep<a name="line.23"></a>
<span class="sourceLineNo">024</span> * track of new objects as they are created. When each object's {@link GraphCloneable} references are copied, the<a name="line.24"></a>
<span class="sourceLineNo">025</span> * {@link GraphCloneRegistry} is used to check whether the referred-to objects have already been copied, and if so, the existing<a name="line.25"></a>
<span class="sourceLineNo">026</span> * copy is used. This requires that implementations {@linkplain GraphCloneRegistry#setGraphClone register} their clones<a name="line.26"></a>
<span class="sourceLineNo">027</span> * prior to {@linkplain GraphCloneRegistry#getGraphClone recursing} on any {@link GraphCloneable} fields.<a name="line.27"></a>
<span class="sourceLineNo">028</span> * &lt;/p&gt;<a name="line.28"></a>
<span class="sourceLineNo">029</span> *<a name="line.29"></a>
<span class="sourceLineNo">030</span> * &lt;p&gt;<a name="line.30"></a>
<span class="sourceLineNo">031</span> * The net effect is equivalent to serializing and then deserializing the entire object graph, but without the overhead,<a name="line.31"></a>
<span class="sourceLineNo">032</span> * losing {@code transient} values, and other issues.<a name="line.32"></a>
<span class="sourceLineNo">033</span> * &lt;/p&gt;<a name="line.33"></a>
<span class="sourceLineNo">034</span> *<a name="line.34"></a>
<span class="sourceLineNo">035</span> * &lt;p&gt;<a name="line.35"></a>
<span class="sourceLineNo">036</span> * Here is an example of a class properly implementing this interface:<a name="line.36"></a>
<span class="sourceLineNo">037</span> *  &lt;pre&gt;<a name="line.37"></a>
<span class="sourceLineNo">038</span> *  // We implement Cloneable so super.clone() will work<a name="line.38"></a>
<span class="sourceLineNo">039</span> *  public class Person implements Cloneable, GraphCloneable {<a name="line.39"></a>
<span class="sourceLineNo">040</span> *<a name="line.40"></a>
<span class="sourceLineNo">041</span> *      // Regular fields<a name="line.41"></a>
<span class="sourceLineNo">042</span> *      private int age;<a name="line.42"></a>
<span class="sourceLineNo">043</span> *      private String lastName;<a name="line.43"></a>
<span class="sourceLineNo">044</span> *      private String firstName;<a name="line.44"></a>
<span class="sourceLineNo">045</span> *      private List&amp;lt;String&amp;gt; nicknames = new ArrayList&amp;lt;String&amp;gt;();<a name="line.45"></a>
<span class="sourceLineNo">046</span> *<a name="line.46"></a>
<span class="sourceLineNo">047</span> *      // GraphCloneable fields - values may be null and/or even refer back to me<a name="line.47"></a>
<span class="sourceLineNo">048</span> *      private Person spouse;<a name="line.48"></a>
<span class="sourceLineNo">049</span> *      private List&amp;lt;Person&amp;gt; friends = new ArrayList&amp;lt;Person&amp;gt;();<a name="line.49"></a>
<span class="sourceLineNo">050</span> *<a name="line.50"></a>
<span class="sourceLineNo">051</span> *      // Getters &amp;amp; setters go here...<a name="line.51"></a>
<span class="sourceLineNo">052</span> *<a name="line.52"></a>
<span class="sourceLineNo">053</span> *      // Our implementation of the GraphCloneable interface<a name="line.53"></a>
<span class="sourceLineNo">054</span> *      &amp;#64;Override<a name="line.54"></a>
<span class="sourceLineNo">055</span> *      public void createGraphClone(GraphCloneRegistry registry) throws CloneNotSupportedException {<a name="line.55"></a>
<span class="sourceLineNo">056</span> *<a name="line.56"></a>
<span class="sourceLineNo">057</span> *          // Create clone and register it with the registry<a name="line.57"></a>
<span class="sourceLineNo">058</span> *          final Person clone = (Person)super.clone();         // this copies all of the simple fields<a name="line.58"></a>
<span class="sourceLineNo">059</span> *          registry.setGraphClone(clone);                      // let the registry know who our clone is<a name="line.59"></a>
<span class="sourceLineNo">060</span> *<a name="line.60"></a>
<span class="sourceLineNo">061</span> *          // Deep copy any non-GraphCloneable fields not already handled by super.clone()<a name="line.61"></a>
<span class="sourceLineNo">062</span> *          clone.nicknames = new ArrayList&amp;lt;String&amp;gt;(this.nicknames);<a name="line.62"></a>
<span class="sourceLineNo">063</span> *<a name="line.63"></a>
<span class="sourceLineNo">064</span> *          // Now copy GraphCloneable fields using registry.getGraphClone()<a name="line.64"></a>
<span class="sourceLineNo">065</span> *          clone.spouse = registry.getGraphClone(this.spouse);<a name="line.65"></a>
<span class="sourceLineNo">066</span> *          clone.friends = new ArrayList&amp;lt;Person&amp;gt;(this.friends.size());<a name="line.66"></a>
<span class="sourceLineNo">067</span> *          for (Person friend : this.friends)<a name="line.67"></a>
<span class="sourceLineNo">068</span> *              clone.friends.add(registry.getGraphClone(friend));<a name="line.68"></a>
<span class="sourceLineNo">069</span> *      }<a name="line.69"></a>
<span class="sourceLineNo">070</span> *  }<a name="line.70"></a>
<span class="sourceLineNo">071</span> *  &lt;/pre&gt;<a name="line.71"></a>
<span class="sourceLineNo">072</span> * &lt;/p&gt;<a name="line.72"></a>
<span class="sourceLineNo">073</span> *<a name="line.73"></a>
<span class="sourceLineNo">074</span> * &lt;p&gt;<a name="line.74"></a>
<span class="sourceLineNo">075</span> * To graph clone any object graph rooted at {@code root}, you would do this:<a name="line.75"></a>
<span class="sourceLineNo">076</span> *  &lt;pre&gt;<a name="line.76"></a>
<span class="sourceLineNo">077</span> *      new GraphCloneRegistry().getGraphClone(root);<a name="line.77"></a>
<span class="sourceLineNo">078</span> *  &lt;/pre&gt;<a name="line.78"></a>
<span class="sourceLineNo">079</span> * &lt;/p&gt;<a name="line.79"></a>
<span class="sourceLineNo">080</span> *<a name="line.80"></a>
<span class="sourceLineNo">081</span> * @see GraphCloneRegistry<a name="line.81"></a>
<span class="sourceLineNo">082</span> */<a name="line.82"></a>
<span class="sourceLineNo">083</span>public interface GraphCloneable {<a name="line.83"></a>
<span class="sourceLineNo">084</span><a name="line.84"></a>
<span class="sourceLineNo">085</span>    /**<a name="line.85"></a>
<span class="sourceLineNo">086</span>     * Create a graph clone of this instance and register it with the given {@link GraphCloneRegistry}.<a name="line.86"></a>
<span class="sourceLineNo">087</span>     *<a name="line.87"></a>
<span class="sourceLineNo">088</span>     * &lt;p&gt;<a name="line.88"></a>
<span class="sourceLineNo">089</span>     * This method should perform a normal "deep copy" operation, but with the following changes:<a name="line.89"></a>
<span class="sourceLineNo">090</span>     * &lt;ul&gt;<a name="line.90"></a>
<span class="sourceLineNo">091</span>     *  &lt;li&gt;<a name="line.91"></a>
<span class="sourceLineNo">092</span>     *      The new clone must be {@linkplain GraphCloneRegistry#setGraphClone registered} with the provided<a name="line.92"></a>
<span class="sourceLineNo">093</span>     *      {@link GraphCloneRegistry} before this method returns.<a name="line.93"></a>
<span class="sourceLineNo">094</span>     *  &lt;/li&gt;<a name="line.94"></a>
<span class="sourceLineNo">095</span>     *  &lt;li&gt;<a name="line.95"></a>
<span class="sourceLineNo">096</span>     *      The {@linkplain GraphCloneRegistry#setGraphClone registration} in the previous step must occur<a name="line.96"></a>
<span class="sourceLineNo">097</span>     *      prior to {@linkplain GraphCloneRegistry#getGraphClone recursing} on any {@link GraphCloneable} fields.<a name="line.97"></a>
<span class="sourceLineNo">098</span>     *  &lt;/li&gt;<a name="line.98"></a>
<span class="sourceLineNo">099</span>     *  &lt;li&gt;<a name="line.99"></a>
<span class="sourceLineNo">100</span>     *      All {@link GraphCloneable} fields must be copied via {@link GraphCloneRegistry#getGraphClone}.<a name="line.100"></a>
<span class="sourceLineNo">101</span>     *  &lt;/li&gt;<a name="line.101"></a>
<span class="sourceLineNo">102</span>     * &lt;/ul&gt;<a name="line.102"></a>
<span class="sourceLineNo">103</span>     * &lt;/p&gt;<a name="line.103"></a>
<span class="sourceLineNo">104</span>     *<a name="line.104"></a>
<span class="sourceLineNo">105</span>     * &lt;p&gt;<a name="line.105"></a>
<span class="sourceLineNo">106</span>     * The most efficient implementation of this method often involves declaring the class to implement {@link Cloneable}<a name="line.106"></a>
<span class="sourceLineNo">107</span>     * and starting with an invocation of {@link Object#clone super.clone()} (the class need not actually override<a name="line.107"></a>
<span class="sourceLineNo">108</span>     * {@link Object#clone}). For that reason, this method is declared to throw {@link CloneNotSupportedException}<a name="line.108"></a>
<span class="sourceLineNo">109</span>     * as a coding convenience; if a {@link CloneNotSupportedException} is actually thrown, it will trigger a<a name="line.109"></a>
<span class="sourceLineNo">110</span>     * {@link RuntimeException}.<a name="line.110"></a>
<span class="sourceLineNo">111</span>     * &lt;/p&gt;<a name="line.111"></a>
<span class="sourceLineNo">112</span>     *<a name="line.112"></a>
<span class="sourceLineNo">113</span>     * &lt;p&gt;<a name="line.113"></a>
<span class="sourceLineNo">114</span>     * This method will only be invoked once for any instance during a graph cloning operation.<a name="line.114"></a>
<span class="sourceLineNo">115</span>     * &lt;/p&gt;<a name="line.115"></a>
<span class="sourceLineNo">116</span>     *<a name="line.116"></a>
<span class="sourceLineNo">117</span>     * @throws NullPointerException if {@code registry} is null<a name="line.117"></a>
<span class="sourceLineNo">118</span>     * @throws CloneNotSupportedException declared so implementors can invoke {@link Object#clone super.clone()}<a name="line.118"></a>
<span class="sourceLineNo">119</span>     *  directly; if thrown, it will trigger a {@link RuntimeException}<a name="line.119"></a>
<span class="sourceLineNo">120</span>     */<a name="line.120"></a>
<span class="sourceLineNo">121</span>    void createGraphClone(GraphCloneRegistry registry) throws CloneNotSupportedException;<a name="line.121"></a>
<span class="sourceLineNo">122</span>}<a name="line.122"></a>
<span class="sourceLineNo">123</span><a name="line.123"></a>




























































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